Basic For loop fails in Solidity

Question

I created a simple For loop that should return an array of numbers. But it fails with errored: VM error: revert

I guess there is something fundamental I am missing here, so I hope you guys can help here.

    // SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

contract ForLoop {


     function getOwnedTokens() public pure returns (uint[] memory) {

        uint[] memory listOfOwnedTokens;

        uint numberOfOwnedTokens = 4;

        for(uint tokenIndex = 0; tokenIndex < numberOfOwnedTokens; tokenIndex++)  {
            listOfOwnedTokens[tokenIndex] = tokenIndex;
         }

        return listOfOwnedTokens;
    }

}

Answer 1

    // SPDX-License-Identifier: GPL-3.0

    pragma solidity >=0.7.0 <0.9.0;

    contract ForLoop {


 function getOwnedTokens() public pure returns (uint[] memory) {
    uint numberOfOwnedTokens = 4;
    uint[] memory listOfOwnedTokens = new uint[](numberOfOwnedTokens);



    for(uint tokenIndex = 0; tokenIndex < numberOfOwnedTokens; tokenIndex++)  {
        listOfOwnedTokens[tokenIndex] = tokenIndex;
     }

    return listOfOwnedTokens;
}

}

Here, i fixed it for you. Its kinda hard to explain the answer. But "it is not allowed" to index unfixed sized array that are memory.